Coding⏱️ 4 min read📅 2026-06-11

How to Fix: A way to capture error output from ffmpeg/avconv in a bash script

Batch convert video files with ffmpeg/avconv and capture error output in a bash script.

Quick Answer: Use the `2>&1` redirection to redirect both stdout and stderr to the same file, allowing you to capture any errors that occur during the conversion process.

📋 Table of Contents

  1. 🔍 Why This Happens
  2. ✅ Best Solutions to Fix It
  3. 💡 Conclusion

The script provided attempts to batch convert various video file formats using ffmpeg/avconv, but it encounters an issue with capturing error output. This problem affects users who rely on the script's ability to monitor and report errors during the conversion process.

Capturing error output from ffmpeg/avconv can be frustrating for batch converters, as it makes it difficult to determine whether a conversion was successful or not. In this troubleshooting guide, we will explore possible causes of this issue and provide solutions to help users overcome it.

🔍 Why This Happens

  • The primary cause of this issue lies in the way ffmpeg/avconv handles error output when used in a bash script. By default, the program does not capture or display errors explicitly, making it challenging for scripts to detect and report them.
  • Another possible reason for this issue is related to the usage of avconv within the script. Specifically, the use of the '-y' option can sometimes cause issues with error reporting.

✅ Best Solutions to Fix It

Capturing Error Output using ffmpeg's -v errorlevel

  1. Step 1: To capture error output from ffmpeg/avconv, you can modify the script to include the '-v errorlevel' option. This will enable verbose mode and display errors during the conversion process.
  2. Step 2: For example, replace the line: `avconv -y -i $file -map 0 -map -0:s -vcodec libx264 -acodec libfaac $dirname/$basename.mp4` with: `ffmpeg -v errorlevel 3 -i $file -map 0 -map -0:s -vcodec libx264 -acodec libfaac $dirname/$basename.mp4`. This will display errors on a scale of 1-5, where 5 indicates fatal errors.
  3. Step 3: By using this approach, you can effectively capture error output from ffmpeg/avconv and improve the reliability of your batch conversion script.

Using stderr Redirection

  1. Step 1: Alternatively, you can use stderr redirection to capture error output. This involves redirecting the standard error stream to a file or another process.
  2. Step 2: For example, add the following line before the conversion command: `2>&1 | tee -a error.log`. This will redirect both stdout and stderr to an error log file named 'error.log'.
  3. Step 3: By using this approach, you can capture error output from ffmpeg/avconv without modifying the original script. However, keep in mind that this method may not provide as much detail as using the '-v errorlevel' option.

💡 Conclusion

In conclusion, capturing error output from ffmpeg/avconv is crucial for reliable batch conversion scripts. By employing one of the two methods outlined above – either using the '-v errorlevel' option or stderr redirection – you can effectively monitor and report errors during the conversion process, ensuring a more robust and efficient script.

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